The heart of a computer is a magnetic disk drive which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Storage (recording) devices in data equipment use semiconductor memory and magnetic memory for data storage. Semiconductor memory is used in internal storage devices due to their quick access time, and magnetic disk devices are used in external storage devices due to their large capacity and non-volatility. Storage capacity is a key indicator of the performance of a magnetic disk device, and with the growth of the information society in recent years, large capacity and compact magnetic disk devices are in increasing demand by the market. Perpendicular recording is possibly the most suitable recording system to meet this demand. In the perpendicular recording system, the direction of magnetization of the recording medium is perpendicular to the medium plane, so the effect of opposing magnetic fields acting between adjacent magnetized areas is small compared to a horizontal recording system. As a result, it is possible to record a high density of magnetic data on the medium, and to create a magnetic disk device with a very large capacity. It is possible that this system will completely replace conventional horizontal recording systems in the near future due to its capacity for high-density storage.
With a perpendicular recording system, it is preferable to increase the gradient of the recording magnetic field generated by the main magnetic pole to achieve a high density of recording. U.S. Pat. No. 4,656,546 discloses a perpendicular recording magnetic head with a magnetic shield having soft magnetic characteristics provided on the trailing side of the main magnetic pole as a means of increasing the gradient of the recording magnetic field. With this magnetic head, the distance between the main magnetic pole and the magnetic shield can be narrowed and material with a high saturation flux density used in the magnetic shield to further increase the recording magnetic field gradient. However, if the distance between the main magnetic pole and the high saturation flux density magnetic shield (the recording gap) is narrowed, much of the magnetic flux from the main magnetic pole flows into the magnetic shield, preventing a strong recording magnetic field from being achieved.
Japanese Unexamined Patent Publication No. 2007-265562 discloses a structure having a perpendicular magnetic recording head comprising a shield laminated in the float direction with a soft magnetic film of different Curie points, wherein a film with a high saturation flux density is positioned on the floating surface in a situation where it receives heat from the coil in a recording state, with the purpose of both suppressing pole erasure and ensuring a strong recording magnetic field.
The aim of the invention cited in Japanese Unexamined Patent Publication No. 2007-265562 is to suppress pole erasure by providing a function whereby the heating effect from the coil is used in the shield to reduce the saturation flux density of the soft magnetic film with a low Curie point and concentrate the flux contributing to the recording magnetic field selectively on the film with a high Curie point positioned on the floating surface, with flux being made to pass through the soft magnetic film with a low Curie point as the temperature drops after recording.
To achieve the above aim, heat is emitted from the coil. A magnetic head for perpendicular magnetic recording has a head structure which is significantly different as compared to an in-plane recording head, with the number of coil windings being 4 or less. For this reason, the resistance of the coil is less than 2Ω within the element, and the temperature rise during recording is held within 10° C., as is known in the art. For this reason, the temperature rise that is useable during recording is within the range of 10° C., thereby rendering it difficult to realize a practical perpendicular magnetic recording head with a shield structure that uses this difference between Curie points.
The reason why the rise in temperature within the element is held to a low level by the restriction on the coil resistance is that the metal of which the element is comprised (having a high coefficient of linear expansion) expands with heat due to the temperature rise of the element, and the degree of float cannot be reduced (preventing an increase in recording density) due to the phenomenon of projection from the floating surface.
Since it is preferable to increase the gradient of the recording magnetic field generated by the main magnetic pole to achieve a high density of recording, and current approaches for maximizing the gradient of the recording magnetic field are limited by difficulties arising from magnetic flux flowing from the pole into the magnetic shield, preventing strong recording magnetic field formation, and element expansion due to heat, a system and/or method for overcoming the limitations of current methods for increasing the recording magnetic field gradient would be very beneficial.